Radio receiving and direction finding apparatus



Jan. 9, 1940. 2,186,867

RADIO RECEIVING AND DIRECTION FINDING APPARATUS J. P. JEFFCZOCKl Filed Aug. 20, 1938 www@ M,

K S @C U MO. N. c M VF w n WF. E MA d Dry B N H o \u Patented Jan. 9, 1940 Neres RADIO RECEIVING AND. DIRECTION FINDING APPARATUS .lohn Parkyn J elcock, Surbiton, England 3 Claims.

This invention relates to radio receiving and direction nding apparatus, including cathode ray type direction finders.

Under the prevailing conditions of Wavelength allocation, radio reception is frequently rendered difcult or impossible by interference from stations operating on similar frequencies. With telegraphic reception, interference may be avoided by using a very high degree of selectivity,

i: but with receiving apparatus proposed heretofore,

there :is then a risk that while receiving a relatively unimportant message, the operator may miss an urgent signal, e. g., from an aircraft or a ship whose transmission is slightly off the cori rect frequency, but possibly within the international tolerance.

With aural type direction nders, a good operator can often obtain bearings and read Morse signals under conditions of severe interference,

l'- by concentrating on the particular heterodyne note which corresponds to the wanted signal. However, with cathode ray type direction finders, aural frequency discrimination is not possible when taking bearings, and consequently, when more than two signals act simultaneously on the electron stream, the resultant image becomes unintelligible, and a bearing cannot be obtained. Thus, in cathode ray type direction finders which are to be used under conditions of severe interl ference, it is essential that extremely sharp selectivity should be provided in the amplifier channels which apply the deflecting voltages to the deilecting mechanism of the cathode ray tube; however, for reasons already explained,

i it is not desirable in the mobile radio services, to have such a high degree of selectivity in the aural monitoring channel of cathode ray type direction finders, because urgent signals might be missed. Thus, the visual channel should have a l very sharp selectivity characteristic. and the aural monitoring channel should have a relatively at selectivity characteristic;consequently, a number of signals having slightly different frequencies, may be heard simultaneously, and when i the tuning control is manipulated, the bearing corresponding to each individual signal will be indicated visually in sequence. However, with cathode ray type direction finders proposed heretofore, it would be diiiicult or impossible for the operator to identify each bearing indication with the corresponding aural signal (telegraphic or telephonic).

One object of the invention is to provide radio receiving or direction finding apparatus, in which l the selectivity characteristic has a relatively fiat (Cl. Z50-11) top (preferably with steep sides) except for` a narrow peak which projects from the centre (or, any other part) of the fiat portion of the characteristic. Thus, the signal to which the receiver is accurately tuned, isn accentuated aurally relative to signals on adjacent frequencies, which are nevertheless audible in the background. Another object of the invention is to provide a cathode ray type direction finder embodying an aural monitoring amplifier having the type of selectivity characteristic described in the preceding paragraph. The amplifiers which supply the visual deecting voltages, should preferably have selectivity characteristics as sharp as the peak in the monitor amplifier characteristic. Thus, the aural signal which corresponds to the' bearing indicated on the screen of the cathode ray tube, is accentuated and thereby identified.

To illustrate one method of obtaining the novel selectivity characteristic, a cathode' ray type direction finder embodying the invention, will now be described with reference to the accompanying drawing in which Fig. 1 shows a vcircuit arrangement, and Figs. 2 4 illustrate characteristic curves. As shown in Fig. l, two components I 2, of a directive aerial system, e. g., Adcock or Bellini Tosi type, are connected to the two pairs of deecting plates in a cathode ray tube 3, through amplifiers A and B having K simple resonant circuits giving very sharp selectivity characteristics as shown in Fig. 2; e. g.,

an attenuation of 6 db. at a bandwidth of 150` cycles per second. To obtain such a high degree of selectivity with stability, each amplier in-` corporates inductances of normal decrement, but embodies two stages of frequency conversion (FC), e. g., from signal frequency to 40 kc./s. and from 40 kc./s. to 5 kc./s. The sense of bearings yis indicated by amplifying the signal voltage from ank omni-directional aerial 4, by a similar highly selective amplifier C, and causing the output voltage (at 5 kc./s.) to reduce the illumination of the unwanted half of the cathode rayl image by applying it to the modulating or focussing cylinder 8. Such apparatus is well known.

After the rst stage of frequency conversion in the sense amplifier C, the 40 kc./s. signal is also amplified by a parallel connected amplifier D (referred to as the monitor amplier) having a band pass characteristic with steep sides and comparatively flat top say about 4 kc./s. Wide at 6 db. attenuation (see Fig. 3). The

output voltages from the monitor amplifier (40 output voltages are combined, the phase relation being such that the two signal components are additive and produce a characteristic as shown in Fig. 4. Provision is made for varying the ratio in which the signals from the sense and monitor amplifiers are combined, but normally the adjustment would be such that the output from the sense amplifier raises the level of the wanted signal by say 10 db. relative to other signals contained in the output from the monitor amplifier. 'Ihe combined signal Voltage is applied to the telephones or loud-speaker" 5 through a low pass filter cutting off at say 2.5 kc./s., after amplification (if necessary) by a common audio frequency amplifier. reception of continuous wave telegraphy (type A1 waves),'a variable heterodyne note is provided by applying to the grids of the two final detector valves in the sense and monitor ampli-,

fiers, the output from a common beat oscillator 5, adjustable between say 3.5 and 6.5 kc./s. The output of the oscillator 1 which supplies the necessary heterodyning voltage (at say kc./s.) to the second frequency changer in the sense amplifier, is also applied in suitable phase relation tothe grid of the final detector in the monitor amplifier, in order that the same heterodyne frequency (0 to 1.5 kc./s.) may be produced in the outputs from the final detectors of the sense and monitor amplifiers. f

It Will, of course, be understood that various modifications may be madewithout departing from the spirit of the invention. For example, the new selectivity characteristic might be obtained by means other than combining the outputs from two circuits, for example by the suitable design of a filter which produces the desired characteristic.

I claim:

For the 1. A radio direction nder comprising in combination a radio receiving channel comprising an amplifier having a highly selective characteristic, a cathode ray tube fed from the output of said amplifier, a second radio .receiving channel comprising an amplifier having a band-pass characteristic with a sharp peak projecting from the flat portion thereof, a sound reproducing device fed from the output of said amplifier of said second receiving channel, and means for .l simultaneously tuning both radio receiving channels with the resonance peaks in the respective circuits coinciding in the frequency spectrum.

2. A cathode ray direction finder comprising a directional aerial system, a radio receiving circuit coupled with said directional aerial system and having a highlyV selective characteristic, a cathode ray tube to which the output from said receiving circuit is fed to indicate the direction of the received signals, an o1nni-directional aerial, a second radio receiving circuit coupled With said omni-directional aerial and having a selectivity characteristic which has a relatively fiat top except for a narrow sharp peak which projects from the flat portion of the characteristic, an aural monitoring sound reproducing device to which the output from said second receiving circuit is fed, and means for simultaneously tuning both receiving circuits with the resonance peaks in the respective circuits coinciding in the frequency spectrum.

3. A cathode ray direction finder as claimed in claim 2., wherein the second radio receiving circuitcomprises two ampliers one of which has a flat top characteristic and the other a highly selective characteristic, and means for feeding the combined outputs of said amplifiers to the aural monitoring sound reproducing dev1ce.

' JOHN PARKYN JEFFCOCK. 

